Dimensionless curvature

To account for small thickness variations between different specimens, the dimensionless curvature rj = 2h kc is used. Note that rj depends directly on material properties through Yc and E and on the nonmechanical loading through (el — e2). 

The dimensionless curvature is used to preclude the influence of small thickness variations between specimens. 

Figure 8.14 Dimensionless curvature development during cure for IM6/3100...

Figure 8.15 Comparison of dimensionless curvature (q) predicted by elastic model and experimental data...

In Figure 8.17 the predicted dimensionless curvature at the end of curing and the experimental data are plotted versus degree of cure for the intermittent cure study. Most of the changes occur in the region above a = 0.8. Up to a = 0.95 and at a = 1, the predictions are very good. Between a = 0.95 and 1, however, the model underpredicts the dimensionless curvature by about 40 percent. This could be the result of various assumptions introduced in the material property models. 

Figure 8.17 Dimensionless curvature development during MRC cycle...

The MRC cycle calls for a 182°C cure temperature. The effect of cure temperature on residual stress was investigated by curing specimens at four other cure temperatures (171, 165, 160, and 149°C) while holding the dwell time (4 hours) constant. In Figure 8.18 the dimensionless curvature for these specimens is plotted versus the cure temperature. The curvature is reduced as the cure temperature is decreased with significant reduction in curvature obtained for dwell temperatures of 165°C or less. The final curvature as predicted by the viscoelastic process model is overlaid with the experimental data in Figure 8.18 and is shown to capture the trend. 

Figure 8.18 Effect of cure temperature on dimensionless curvature [model and experimental results]...

Figure 8.19 Dimensionless curvature (a) and weight loss (b) after postcure of partially cured specimens...

Mechanical testing of the three-step cure specimens indicated that no sacrifice in properties resulted from the modification of the process cycle. The retainment of mechanical properties (transverse strength and modulus) coupled with the reduction in dimensionless curvature for the three-step cure cycles investigated provides another suitable cure cycle modification for reduction of residual stresses in composite materials. Overall processing time has not been increased beyond that specified in the MRC cycle. Thus, with no increase in process time and comparable mechanical properties, the residual stresses have been reduced by more than 20 percent in comparison to the MRC cycle baseline data. 

Figure 8.21 Dimensionless curvature (tf) for MRC and three-step cure cycles...

ABSTRACT The characteristic of turbulent flow in jackets with triangular helical ducts was simulated and the velocity fields of fully developed turbulent fluid flow in the jackets were obtained. The features of the local coefficient of resistance C/Reiocai) on outer walls and inner wall were summed up and the effects of dimensionless curvature ratio and Reynolds number on the flow field and the flow resistance were analyzed. The results indicate that the structure of secondary flow is with two steady vortices at turbulent flow conditions. The distribution of/ eiocai on the outer walls differs from that of/ eiocai on the inner wall. The mean coefficient of resistance (/Rem) on the outer walls is about 1.41 1.5 7 times as much as that on the iimer wall. With the increase of dimensionless curvature ratio or Reynolds number,/Rem on the boundary walls increases. 

The dimensionless curvature of the interface, which appears in eq. (32), is given by... 

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